1. Field of the Invention
The invention relates to an apparatus for controlling medium flow, especially for controlling dilution liquid flow in connection with the headbox of a paper-making machine or a cardboard-manufacturing machine, which apparatus comprises a valve which controls dilution flow, which valve consists of a valve housing, a stem part and a flow channel between an inlet and an outlet of the valve.
2. Description of Background Art
Dilution valves are utilised for controlling the flow of dilution liquid to stock flow. Dilution flow may be clean or fibre-bearing water. Dilution water may be, for example, tail water taken from the web as retention. Solutions are known in which, a rotatable valve stem is used in the dilution valve which stem may be rotatable to different control positions for controlling the dilution flow starting from the valve. Such solution is presented in, inter alia, specification FI110879B. However, different problems occur in these solutions. Because there is fines included in the tail water, there is a strong possibility of the valve stem getting blocked in the rotatable valve, especially when dilution water reaches between the stem and the valve body. Such solutions require an extremely strong actuator to rotate the stem. In addition, frequent so-called wash moving of the stem is typically required in order to prevent the blocking of the stem. In addition, the solution requires utilising extremely precise tolerances, whereby the solution becomes manufacturing-technically demanding and expensive to manufacture. Typically, the solution requisites utilising an actuator adapted for the use in question, which frequently increases costs. Furthermore, the flow range of the dilution valves in question is fixed. Equivalent problems occur also in a solution presented in specification FI100895B, in which the flow path is formed to the stem which is moved to and fro, and in which the choke is controlled on the side of the valve inlet.
The object of this invention is to achieve a totally novel solution for a dilution valve, whereby the disadvantages of known prior-art are avoided.